There is growing interest in the idea of light-weight access points, where a wireless LAN (Local Area Network) consists of a number of cheap and simple base station devices, also known as access points or APs connected to a central access router or AR. The AR is responsible for forwarding of data received by the APs to the wider network, and can also perform network management functions. Evidence of the level of interest is the formation of an IETF (Internet Engineering Task Force) study group who are producing a draft for LWAPP (light-weight access point protocol).
One of the cited advantages of the light-weight access point configuration is that, other than allowing the individual access points to be less complex, MAC-layer information such as RSSI (received signal strength indications) for received packets or messages can be passed to the central AR and used for decisions on network management, e.g. load balancing and handover decisions. It is clear that these types of decision. can only be made if knowledge of the entire network status including signal quality, e.g. RSSI is available.
One of the issues in using RSSI information as a basis for network management is to be able to link the RSSI information with a particular station. However, this in itself is not enough since a station may send different frames at different power levels depending on the situation, and movement of a station may also cause different frames to be received with different power levels. Also, transmission errors such as collisions may mean that one AP may successfully receive a transmission while another AP does not. All of the above indicate that one must only compare RSSI indications for the same frame transmission in order to be able to make meaningful assessments.
It has been proposed that an AP could send RSSI measurements along with data frames received from a station. If more than one AP receives a transmission, the RSSI can in principle be compared.
A primary drawback with the proposed solution is that, in itself, the received data frame does not necessarily contain sufficient information to uniquely identify the transmission. In the case of an IEEE 802.11 WLAN (wireless Local Area Network), the address of the transmitter is encoded in the transmitted frame, along with a packet sequence number and a flag to indicate a retransmission. However, if more than a single retransmission of the frame is performed it is no longer possible to distinguish between subsequent transmitted frames.
A secondary drawback with the proposed solution is that the amount of data transmitted over the network between the access points and the access router is multiplied by the number of access points, receiving the transmitted frame or message, which generates a substantial network load.